1. Technical Field
This invention relates to reflective telescope systems and, more particularly, to an all-reflective zoom optical system.
2. Discussion
The performance of conventional high quality telescopes when used on the earth for celestial viewing is principally limited to the earth's atmosphere rather than by the construction of the telescopes. Atmospheric effects not only limit the resolution of a telescope, but also absorb large portions of the electromagnetic spectral range. While in the past, little could be done about this limitation, today, with the help of earth satellites and other space vehicles, it is possible to place a telescope above the atmosphere and perform extraterrestrial observations without interference from it. As a result, there has arisen a need for a telescope which can more fully take advantage of this new environment. Also, it should be understood that the present invention may be utilized for other airborne or ground based applications that require viewing distant objects. This invention may also be used to transmit radiation.
The advantages of zoom optical systems are well known to those skilled in the art. However, virtually all of the known zoom optical systems utilize refractive optical elements in whole or in part. Refractive optical elements generally have one or more of the following disadvantages. Refractive systems generally have spectral limitations and chromatic aberrations. Refractive systems have size limitations, lens material limitations and a lack of radiation hardness. Refractive systems prohibit simultaneous multi-spectral operations in widely separated portions of the electromagnetic spectral range. Further, the refractive systems are sensitive to thermal changes and are exceptionally heavy when used in large aperture designs.